Use of associative thickeners based on polyurethane and/or dipropylene glycol monoalkyl ethers in colored and/or decorative effect multi-layered lacquers

ABSTRACT

Use of associative thickeners based on polyurethane and/or dipropylene glycol monoalkyl ethers for suppressing defects in color and/or effect multicoat paint systems, or their touch-up paints.

This application is a National Phase Application of Patent ApplicationPCT/EP00/08503 filed on 31 Aug. 2000.

The present invention relates to the use of polyurethane-basedassociative thickeners and/or dipropylene glycol monoalkyl ethers tosuppress optical defects in multicoat color and/or effect paint systemsor their refinishes. The present invention also relates to novel aqueousbasecoat materials which comprise at least one polyurethane-basedassociative thickener and/or at least one dipropylene glycol monoalkylether. The present invention further relates to the use of the novelaqueous basecoat materials for producing multicoat color and/or effectpaint systems and their refinishes.

Owing to their numerous advantageous properties, multicoat color and/oreffect paint systems are nowadays employed in many fields, examplesbeing the coating of motor vehicle bodies, industrial components,including electrical components, coils, and packaging, and fabrics orfurniture. Owing to the particularly stringent requirements on the partof automakers and their customers, these multicoat color and/or effectpaint systems have become established in particular in this field ofuse.

As is known, the bodies of automobiles are nowadays coated with amulticoat paint system composed of a primer, particularly anelectrocoat, a surfacer or an antistonechip primer, and a multicoatcolor and/or effect paint system. The multicoat paint system itself isgenerally composed of at least one basecoat and at least one clearcoat.Advantageously, the basecoat is produced from an aqueous basecoatmaterial. In accordance with the particularly advantageous wet-on-wettechnique, the aqueous basecoat material is applied to the surfacer orthe antistonechip primer and partly dried, but not crosslinked.Thereafter, at least one clearcoat film is applied to the uncuredaqueous basecoat film and is cured together with the aqueous basecoatfilm. This technique is also employed for the refinish of the multicoatcolor and/or effect paint systems.

Both during the production of the multicoat color and/or effect paintsystems and during the refinish of defects present therein, opticaldefects can occur which are manifested to disruptive effect and whichgive cause for complaints. These optical defects may have a variety ofcauses.

Accordingly, defects in the surfacer or in the antistonechip primer arenormally removed by abrading. When this is done, abrasion dust residuesin the form of fingerprints or, in the case of wet abrasion, in the formof dried water droplets can remain. After overcoating with aqueousbasecoat and clearcoat material, these “fingerprints” and/or “droplets”show up as light-colored, clearly visible sites in the resultingmulticoat color and/or effect paint system. These optical defects arealso referred to by the skilled worker as “light spots”.

Optical defects of this kind also arise if the clearcoat of a multicoatcolor and/or effect paint system is abraded for purposes of betteradhesion of a refinish that is to be applied. These optical defects arealso referred to by the skilled worker as “abrasion spots”.

These pale spots are not abrasion scars which are poorly covered, butmay instead be induced even by beads of sweat or the sweat on thefingers.

Another kind of optical defect, known as polishing spots, results if thefinished multicoat color and/or effect paint system is polished atdamaged sites, but then, owing to further damaged sites, has to besubjected to a complete refinish, with the polished sites as well beingovercoated. In the refinish, these polishing sites are very clearlyvisible owing to their different shade.

To date it has been possible to prevent these optical defects only byextremely careful and cautious working and a high additional cleaningeffort, since the aqueous basecoat materials available at present do nothave the sufficient insensitivity to such defects in and on thesurfacers and/or in and on the multicoat color and/or effect paintsystems, and are therefore unable, or unable sufficiently, to compensatethese defects optically. This fact, however, leads to relatively longprocessing times and thus to higher costs in line finishing or in lineor workshop refinish.

There is therefore a high demand for basecoat materials, especiallyaqueous basecoat materials, which no longer have these disadvantages butInstead provide optical compensation of the defects while retaining allof their other advantageous properties, if not indeed improving uponthem.

Aqueous basecoat materials which are outstandingly suitable forproducing color and/or effect paint systems are known, for example, fromthe German patent application DE-A-44 37 535. They comprise an inorganicthickener, such as a phyllosilicate, and organic solvents, such as butylglycol. As binders they comprise water-soluble or -dispersiblepolyurethanes, water-soluble or -dispersible polyacrylate resinsprepared in the presence of such polyurethanes, and 3water-soluble or-dispersible polyesters. They have a very high storage stability even atrelatively high temperatures. The use of polyurethane-based associativethickeners and/or dipropylene glycol monoalkyl ethers is not disclosedby DE-A-44 37 535.

Polyurethane-based associative thickeners and their performanceproperties and advantages are known. By way of example, reference may bemade here to Römpp Lexikon Lacke und Druckfarben, Georg Thieme Verlag,Stuttgart, N.Y., 1998, “thickeners”, pages 599 to 600, and the textbook“Lackadditive” [Additives for Coatings] by Johan Bieleman, Wiley-VCH,Weinheim, N.Y., 1998, pages 51 to 59 and 65. The use of thesepolyurethane-based associative thickeners for suppressing opticaldefects in multicoat color and/or effect paint systems and theirrefinishes are not described therein.

It is an object of the present invention to [lacuna] novel basecoatmaterials, especially the aqueous basecoat materials, which comprisenovel combinations of constituents and which allow the production andrefinish of multicoat color and/or effect paint systems without theformation of light spots or polishing spots. The novel basecoatmaterials, particularly the novel aqueous basecoat materials, ought tocontinue to have the particular advantages of the existing basecoatmaterials or to exhibit additional, novel advantageous properties.

Found accordingly was the novel use of polyurethane-based associativethickeners and/or dipropylene glycol monoalkyl ethers for suppressingoptical defects in multicoat color and/or effect paint systems and theirrefinishes.

In the text below, this novel use is referred to as “inventive use”.

Additionally found was the novel aqueous basecoat material whichcomprises

-   -   (A) at least one water-soluble or -dispersible polyurethane,    -   (B) at least one crosslinking agent,    -   (C) at least one color and/or effect pigment,    -   (D) at least one neutralizing agent,    -   (E) at least one inorganic thickener, and    -   (F) at least one dipropylene glycol monoalkyl ether.

Additionally found was the further novel aqueous basecoat material whichcomprises

-   -   (A) at least one water-soluble or -dispersible polyurethane,    -   (B) at least one crosslinking agent,    -   (C) at least one color and/or effect pigment,    -   (D) at least one neutralizing agent,    -   (E) at least one inorganic thickener,    -   (G) at least one polyurethane-based associative thickener,    -   (H) if desired, at least one water-soluble or -dispersible        polyacrylate resin prepared in the presence of a water-soluble        or -dispersible polyurethane, and    -   (I) at least one water-soluble or -dispersible polyester resin.

In the text below, these novel aqueous basecoat materials are referredto collectively as “aqueous basecoat materials of the invention”.

Found not least were the novel multicoat color and/or effect paintsystems which comprises at least one basecoat producible from one of theaqueous basecoat materials of the invention.

In the light of the prior art it was surprising and unforeseeable forthe skilled worker that the object of the present invention could beachieved by means of the inventive use. Even more surprising was thatthe achievement of the object was demonstrably not based on theTheological properties of the aqueous basecoat materials of theinvention, which in this respect are equivalent to the known aqueousbasecoat materials. Moreover, it could not at all have been expectedthat the durable suppression or prevention of polishing spots could beachieved by the combination of the polyurethane-based associativethickener (G) for inventive use and at least one dipropylene glycolmonoalkyl ether (F).

In accordance with the invention, the polyurethane-based associativethickener (G) or the dipropylene glycol monoalkyl ether (F) can beemployed alone, with the use alone of the associative thickener (G)offering particular advantages and therefore being preferred inaccordance with the invention very particular advantages result,however, from the joint use of the two constituents, which is thereforeparticularly preferred in accordance with the invention.

The first inventively essential constituent of the aqueous basecoatmaterials of the invention is therefore at least one polyurethane-basedassociative thickener (G). These thickeners are normally composed ofnonionic hydrophobic polymers which are available either in liquid form,as a 50 percent strength solution in water or in organic solvents, forexample, or in powder form. They are based on water-solublepolyurethanes having a comparatively low molecular weight of from 10 000to 50 000.

The water-soluble polyurethanes (G) are prepared by reactingdiisocyanates, especially the diisocyanates described below, with diols,especially the diols described below, and hydrophobic blockingcomponents, thereby resulting in the following idealized structure ofthe general formula I.R¹—NH—C(O)—(—OCH₂CH₂—)_(x)—[O—C(O)—NH—R²—NH—C(O)—(—OCH₂CH₂—)_(x)—]_(n)—O—C(O)—NH—R¹  (I)

In the general formula I, the indices x and n stand for integers whosevalue is sufficient to give the molecular weights indicated above.

The radical R¹ stands for a hydrophobic aliphatic or aromatic group.Examples of suitable groups of this kind are oleyl, stearyl,dodecylphenyl or nonylphenyl.

The radical R² stands for a hydrophilic segment. Examples of suitablehydrophilic segments are polyesters, especially polyesters of maleicacid and ethylene glycol, and polyethers, especially polyethylene glycolor its derivatives.

The polyurethane-based associative thickeners for inventive usetherefore contain the three following kinds of segments orbuilding-block groups:

-   -   hydrophobic end segments,    -   two or more hydrophilic segments, and    -   urethane groups.

These segments or building-block groups can be linked to one another ina very wide variety of ways, so resulting in a very wide variety ofpolymer structures. In accordance with the invention, however,advantageous associative thickeners are those which contain linear andcomb-shaped polymer structures. It is essential that each polymermolecule contains at least two hydrophobic end segments.

For the preparation of the aqueous basecoat materials of the invention,the associative thickeners (G) for inventive use are employed as powdersor, preferably, as 20 to 30% strength by weight solutions in at leastone water-dilutable solvent.

In the aqueous basecoat materials of the invention they areadvantageously present in an amount of from 0.1 to 4.0%, preferably from0.4 to 3.5%, and in particular from 0.4 to 3.0% by weight, based in eachcase on the overall weight of the respective aqueous basecoat material.

Dipropylene glycol monoalkyl ethers are compounds which are known per seand are employed in the coatings field as solvents or as solventadditions. Examples of suitable alkyl radicals in this context aremethyl, propyl, isopropyl, n-butyl, n-pentyl or n-hexyl, of which themethyl radical is particularly advantageous and is therefore used withparticular preference.

The dipropylene glycol methyl ether (F) used with particular preferenceis a compound known per se or a mixture known per se, both of which areavailable commercially. It is derived from dipropylene glycol,1,1′-oxybis-(2-propanol), and/or isomers thereof.

In the aqueous basecoat materials of the invention, the dipropyleneglycol monoalkyl ethers (F) are present advantageously in an amount offrom 0.5 to 11%, preferably from 1.0 to 9%, and in particular from 1.0to 7.0% by weight, based in each case on the overall weight of therespective aqueous basecoat material.

The other essential constituent of the aqueous basecoat materials of theinvention is at least one water-soluble or -dispersible polyurethane(A). Polyurethanes (A) and processes for preparing them are known per seand are described, for example, in the German patent DE-A-44 37 535.

Advantageously, depending on the nature of the stabilization, thepolyurethane (A) for inventive use has an acid number or amine number offrom 10 to 250 mg KOH/g (ionic stabilization or nonionic plus ionicstabilization) or from 0 to 10 mg KOH/g (nonionic stabilization), an OHnumber of from 30 to 350 mg KOH/g, and a number-average molecular weightof from 1 500 to 55 000 daltons.

For the preparation of the polyurethanes (A) it is conventional to usediisocyanates and also, if desired and in minor amounts,polyisocyanates, for the purpose of introducing branches. In the contextof the present invention, minor amounts are amounts which do not causegelling of the polyurethanes (A) during their preparation. This may alsobe prevented by using small amounts of monoisocyanates as well.

Examples of suitable diisocyanates are isophorone duisocyanate (i.e.,5-isocyanato-1-isocyanatomethyl-1,3,3-trimethylcyclohexane),5-isocyanato-1-(2-isocyanatoeth-1-yl)-1,3,3-trimethylcyclohexane,5-isocyanato-1-(3-isocyanatoprop-1-yl)-1,3,3-trimethylcyclohexane,5-isocyanato-(4-isocyanatobut-1-yl)-1,3,3-trimethylcyclohexane,1-isocyanato-2-(3-isocyanatoprop-1-yl)-cyclohexane,1-isocyanato-2-(3-isocyanatoeth-1-yl)-cyclohexane,1-isocyanato-2-(4-isocyanatobut-1-yl)-cyclohexane,1,2-diisocyanatocyclobutane, 1,3-diisocyanatocyclobutane,1,2-diisocyanatocyclopentane, 1,3-diisocyanatocyclopentane,1,2-diisocyanatocyclohexane, 1,3-diisocyanatocyclohexane,1,4-diisocyanatocyclohexane, dicyclohexylmethane 2,4′-diisocyanate,trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylenediisocyanate, hexamethylene diisocyanate, ethylethylene diisocyanate,trimethylhexane diisocyanate, heptanemethylene diisocyanate ordiusocyanates derived from dimeric fatty acids, as marketed under thecommercial designation DDI 1410 by the company Henkel and described inpatents DO 97/49745 and WO 97/49747, especially2-heptyl-3,4-bis(9-isocyanatononyl)-1-pentylcyclohexane, or 1,2-, 1,4-or 1,3-bis(isocyanatomethyl)cyclohexane, 1,2-, 1,4- or1,3-bis(2-isocyanatoeth-1-yl)cyclohexane,1,3-bis(3-isocyanatoprop-1-yl)cyclohexane, 1,2-, 1,4- or1,3-bis(4-isocyanatobut-1-yl)cyclohexane, liquidbis(4-isocyanatocyclohexyl)methane with a trans/trans content of up to30% by weight, preferably 25% by weight, and in particular 20% byweight, as is described in patents DE-A-44 14 032, GB-A-1 220 717,DE-A-16 18 795 or DE-A-17 93 785; tolylene diisocyanate, xylylenediisocyanate, bisphenylene diisocyanate, naphthylene diisocyanate ordiphenylmethane diisocyanate.

Examples of suitable polyisocyanates are the isocyanurates of thediisocyanates described above.

Examples of highly suitable monoisocyanates are phenyl isocyanate,cyclohexyl isocyanate or stearyl isocyanate.

The polyurethanes (A) for inventive use are also prepared using

-   -   saturated and unsaturated polyols of relatively high and low        molecular mass, especially diols and, in minor amounts, triols        for the purpose of introducing branches,    -   polyamines,    -   amino alcohols, and    -   compounds which introduce stabilizing (potentially) ionic and/or        nonionic functional groups.

Examples of suitable polyols are saturated or olefinically unsaturatedpolyester polyols which are prepared by reacting

-   -   unsulfonated or sulfonated saturated and/or unsaturated        polycarboxylic acids or their esterifiable derivatives, alone or        together with monocarboxylic acids, and    -   saturated and/or unsaturated polyols, alone or together with        monools.

Examples of suitable polycarboxylic acids are aromatic, aliphatic andcycloaliphatic polycarboxylic acids. Preference is given to the use ofaromatic and/or aliphatic polycarboxylic acids.

Examples of suitable aromatic polycarboxylic acids are phthalic acid,isophthalic acid, terephthalic acid, phthalic, isophthalic orterephthalic acid monosulfonate, or halophthalic acids, such astetrachlorophthalic or tetrabromophthalic acid, among which isophthalicacid is advantageous and is therefore used with preference.

Examples of suitable acyclic aliphatic or unsaturated polycarboxylicacids are oxalic acid, malonic acid, succinic acid, glutaric acid,adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid,undecanedicarboxylic acid or dodecanedicarboxylic acid, or dimeric fattyacids, or maleic acid, fumaric acid or itaconic acid, of which adipicacid, glutaric acid, azelaic acid, sebacic acid, dimeric fatty acids andmaleic acid are advantageous and are therefore used with preference.

Examples of suitable cycloaliphatic and cyclic unsaturatedpolycarboxylic acids are 1,2-cyclobutanedicarboxylic acid,1,3-cyclobutanedicarboxylic acid, 1,2-cyclopentanedicarboxylic acid,1,3-cyclopentanedicarboxylic acid, hexahydrophthalic acid,1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid,4-methylhexahydrophthalic acid, tricyclodecanedicarboxylic acid,tetrahydrophthalic acid or 4-methyltetrahydrophthalic acid. Thesedicarboxylic acids may be used both in their cis and in their trans formand also as a mixture of both forms.

Also suitable are the esterifiable derivatives of the abovementionedpolycarboxylic acids, such as their monoesters or polyesters withaliphatic alcohols having 1 to 4 carbon atoms or hydroxy alcohols having1 to 4 carbon atoms, for example. It is also possible to use theanhydrides of the abovementioned polycarboxylic acids, where they exist.

Together with the polycarboxylic acids it is also possible if desired touse monocarboxylic acids, such as, for example, benzoic acid,tert-butylbenzoic acid, lauric acid, isononanoic acid, fatty acids ofnaturally occurring oils, acrylic acid, methacrylic acid, ethacrylicacid or crotonic acid. The preferred monocarboxylic acid used isisononanoic acid.

Examples of suitable polyols are diols and triols, especially diols.Normally, triols are used alongside the diols in minor amounts in orderto introduce branches into the polyester polyols. In the context of thepresent invention, minor amounts are amounts which do not cause gellingof the polyester polyols during their preparation.

Suitable diols are ethylene glycol, 1,2- or 1,3-propanediol, 1,2-, 1,3-or 1,4-butanediol, 1,2-, 1,3-, 1,4- or 1,5-pentanediol, 1,2-, 1,3-,1,4-, 1,5- or 1,6-hexanediol, neopentyl hydroxypivalate, neopentylglycol, diethylene glycol, 1,2-, 1,3- or 1,4-cyclohexanediol, 1,2-, 1,3-or 1,4-cyclohexanedimethanol, trimethylpentanediol,ethylbutylpropanediol or the positionally isomeric diethyloctanediols.These diols may also be used per se for the preparation of thepolyurethanes (A) for inventive use.

Further examples of suitable diols are diols of the formula I or II:

-   -   where R³ and R⁴ are each an identical or different radical and        are an alkyl radical having 1 to 18 carbon atoms, an aryl        radical or a cycloaliphatic radical, with the proviso that R³        and/or R⁴ must not be methyl;

where R⁵, R⁶, R⁸ and R⁹ are each identical or different radicals and arean alkyl radical having 1 to 6 carbon atoms, a cycloalkyl radical or anaryl radical and R⁷ is an alkyl radical having 1 to 6 carbon atoms, anaryl radical or an unsaturated alkyl radical having 1 to 6 carbon atoms,and n is either 0 or 1.

Suitable diols I of the general formula I are all propanediols of theformula in which either R³ or R⁴, or R³ and R⁴, is or are not methyl,such as, for example, 2-butyl-2-ethyl-1,3-propanediol,2-butyl-2-methyl-1,3-propanediol, 2-phenyl-2-methyl-1,3-propanediol,2-propyl-2-ethyl-1,3-propanediol, 2-di-tert-butyl-1,3-propanediol,2-butyl-2-propyl-1,3-propanediol,1-dihydroxymethylbicyclo[2.2.1]heptane, 2,2-diethyl-1,3-propanediol,2,2-dipropyl-1,3-propanediol or 2-cyclo-hexyl-2-methyl-1,3-propanediol,et cetera.

Examples of diols II of the general formula II that may be used are2,5-dimethyl-2,5-hexanediol, 2,5-diethyl-2,5-hexanediol,2-ethyl-5-methyl-2,5-hexanediol, 2,4-dimethyl-2,4-pentanediol,2,3-dimethyl-2,3-butanediol, 1,4-(2′-hydroxypropyl)benzene and1,3-(2′-hydroxypropyl)benzene.

Of these diols, hexanediol and neopentyl glycol are particularlyadvantageous and are therefore used with particular preference.

The abovementioned diols may also be used per se to prepare thepolyurethanes (A) for inventive use.

Examples of suitable triols are trimethylolethane, trimethylolpropane orglycerol, especially trimethylolpropane.

The abovementioned triols may also be used per se to prepare thepolyurethanes (A) for inventive use (cf. the patent EP-A-0 339 433).

If desired, minor amounts of monools may also be used. Examples ofsuitable monools are alcohols or phenols such as ethanol, propanol,n-butanol, sec-butanol, tert-butanol, amyl alcohols, hexanols, fattyalcohols, allyl alcohol, or phenol.

The polyester polyols may be prepared in the presence of small amountsof a suitable solvent as entrainer. Examples of entrainers used arearomatic hydrocarbons, such as especially xylene and (cyclo)aliphatichydrocarbons, e.g., cyclohexane or methylcyclohexane.

Further examples of suitable polyols are polyester diols which areobtained by reacting a lactone with a diol. They are notable for thepresence of terminal hydroxyl groups and repeating polyester fractionsof the formula —(—CO—(CHR¹⁰)_(m)—CH₂—O—)—. Here, the index m ispreferably from 4 to 6 and the substituent R¹⁰ is hydrogen or an alkyl,cycloalkyl, or alkoxy radical. No substituent contains more than 12carbon atoms. The total number of carbon atoms in the substituent doesnot exceed 12 per lactone ring. Examples are hydroxycaproic acid,hydroxybutyric acid, hydroxydecanoic acid, and/or hydroxystearic acid.

Preferred for the preparation of the polyester diols is theunsubstituted ###-caprolactone, where m is 4 and all R¹⁰ substituentsare hydrogen. The reaction with lactone is started by low molecular masspolyols such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, ordimethylolcyclohexane. It is also possible, however, to react otherreaction components, such as ethylenediamine, alkyldialkanolamines, orelse urea, with caprolactone. Other suitable diols of relatively highmolecular mass are polylactam diols, which are prepared by reacting, forexample, ###-caprolactam with low molecular mass diols.

Further examples of suitable polyols include polyether polyols,especially those having a number-average molecular weight of from 400 to5 000, in particular from 400 to 3 000. Examples of highly suitablepolyether diols are polyether diols of the general formulaH—(—O—(CHR¹¹)_(o)—)_(p)OH, where the substituent R¹¹ is hydrogen or alower, unsubstituted or substitued alkyl radical, the index o is from 2to 6, preferably from 3 to 4, and the index p is from 2 to 100,preferably from 5 to 50. Especially suitable examples are linear orbranched polyether diols such as poly(oxyethylene) glycols,poly(oxypropylene) glycols, and poly(oxybutylene) glycols.

The polyether diols ought on the one hand not to introduce excessiveamounts of ether groups, since otherwise the polyurethanes (A) forinventive use that are formed start to swell in water. On the otherhand, they can be used in amounts which ensures the nonionicstabilization of the polyurethanes (A). In that case they serve as thefunctional nonionic groups (a3) described below.

The polyurethane (A) for inventive use comprises alternatively

-   -   (a1) functional groups convertible into cations by neutralizing        agents and/or quaternizing agents, and/or cationic groups,        especially ammonium groups,        or    -   (a2) functional groups convertible into anions by neutralizing        agents, and/or anionic groups, especially carboxylic acid and/or        carboxylate groups,        and/or    -   (a3) nonionic hydrophilic groups, especially poly(alkylene        ether) groups.

Examples of suitable functional groups (a1) for inventive use andconvertible into cations by neutralizing agents (D) and/or quaternizingagents are primary, secondary or tertiary amino groups, secondarysulfide groups or tertiary phosphine groups, especially tertiary aminogroups or secondary sulfide groups.

Examples of suitable cationic groups (a1) for inventive use are primary,secondary, tertiary or quaternary ammonium groups, tertiary sulfoniumgroups or quaternary phosphonium groups, preferably quaternary ammoniumgroups or quaternary ammonium groups, tertiary sulfonium groups, butespecially tertiary sulfonium groups.

Examples of suitable functional groups (a2) for inventive use andconvertible into anions by neutralizing agents (D) are carboxylic acid,sulfonic acid or phosphonic acid groups, especially carboxylic acidgroups.

Examples of suitable anionic groups (a2) for inventive use arecarboxylate, sulfonate or phosphonate groups, especially carboxylategroups.

Examples of suitable neutralizing agents (D) for functional groups (a1)convertible into cations are organic and inorganic acids such as formicacid, acetic acid, lactic acid, dimethylolpropionic acid, citric acid,sulfuric acid, hydrochloric acid or phosphoric acid.

Examples of suitable neutralizing agents (D) for functional groups (a2)convertible into anions are tertiary amines, such as trimethylamine,triethylamine, tributylamine, dimethylaniline, diethylaniline,triphenylamine, dimethylethanolamine, diethylethanolamine,methyldiethanolamine or triethanolamine, for example. Neutralization maytake place in organic phase or in aqueous phase. A preferredneutralizing agent used is dimethylethanolamine.

The total amount of neutralizing agent (D) used in the aqueous basecoatmaterial of the invention is chosen so that from 1 to 100 equivalents,preferably from 50 to 90 equivalents, of the functional groups (a1) or(a2) of the polyurethane (A) for inventive use are neutralized.

Of these functional (potentially) ionic groups (a1) and (a2) andfunctional nonionic groups (a3), the (potentially) anionic groups (a2)are advantageous and are therefore used with particular preference.

The introduction of (potentially) anionic groups (a2) into thepolyurethane molecules takes place by way of the incorporation ofcompounds which contain in the molecule at least one isocyanate-reactivegroup and at least one group capable of forming anions; the amount to beused may be calculated from the target acid number.

Examples of suitable compounds of this kind are those containing twoisocyanate-reactive groups in the molecule. Suitable isocyanate-reactivegroups are, in particular, hydroxyl groups, and also primary and/orsecondary amino groups. Accordingly it is possible, for example, to usealkanoic acids having two substituents on the ###-positioned carbonatom. The substituent may be a hydroxyl group, an alkyl group, or,preferably, an alkylol group. These alkanoic acids have at least one,generally from 1 to 3, carboxyl groups in the molecule. They have 2 toabout 25, preferably 3 to 10, carbon atoms. Examples of suitablealkanoic acids are dihydroxypropionic acid, dihydroxysuccinic acid, anddihydroxybenzoic acid. A particularly preferred group of alkanoic acidsare the ###,###-dimethylolalkanoic acids of the general formulaR¹²—C(CH₂OH)₂COOH, R¹² being a hydrogen atom or an alkyl group having upto about 20 carbon atoms. Examples of especially suitable alkanoic acidsare 2,2-dimethylolacetic acid, 2,2-dimethylolpropionic acid,2,2-dimethylolbutyric acid, and 2,2-dimenthylolpentanoic acid. Thepreferred dihydroxyalkanoic acid is 2,2-dimethylolpropionic acid.Examples of compounds containing amino groups are ###,###-diaminovalericacid, 3,4-diaminobenzoic acid, 2,4-diaminotoluenesulfonic acid, and2,4-diaminodiphenyl ether sulfonic acid.

Stabilizing nonionic poly(oxyalkylene) groups (a3) may be introduced aslateral or terminal groups into the polyurethane molecules. For thispurpose it is possible to use, for example, alkoxypoly(oxyalkylene)alcohols having the general formula R¹³O—(—CH₂—CHR¹⁴—O—)_(r)H, where R¹³is an alkyl radical having 1 to 6 carbon atoms, R¹⁴ is a hydrogen atomor an alkyl radical having 1 to 6 carbon atoms, and the index r is anumber between 20 and 75. (cf. the patents EP-A-0 354 261 or EP-A-0 424705).

The use of polyols, polyamines and amino alcohols leads to an increasein the molecular weight of the polyarethanes (A).

Suitable polyols for the chain extension are polyols containing up to 36carbon atoms per molecule, such as ethylene glycol, diethylene glycol,triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol,1,2-butylene glycol, 1,6-hexanediol, trimethylolpropane, castor oil orhydrogenated castor oil, di-trimethylolpropane ether, pentaerythritol,1,2-cyclohexanediol, 1,4-cyclohexanedimethanol, bisphenol A, bisphenolF, neopentyl glycol, neopentyl glycol hydroxypivalate, hydroxyethylatedor hydroxypropylated bisphenol A, hydrogenated bisphenol A or mixturesthereof (cf. patents EP-A-0 339 433, EP-A-0 436 941, EP-A-0 517 707).

Examples of suitable polyamines have at least two primary and/orsecondary amino groups. Polyamines are essentially alkylene polyamineshaving 1 to 40 carbon atoms, preferably about 2 to 15 carbon atoms. Theymay carry substituents which have no hydrogen atoms that are reactivewith isocyanate groups. Examples are polyamines having a linear orbranched aliphatic, cycloaliphatic or aromatic structure and at leasttwo primary amino groups.

Diamines include hydrazine, ethylenediamine, propylenediamine,1,4-butylenediamine, piperazine, 1,4-cyclohexyldimethylamine,1,6-hexamethylenediamine, trimethylhexamethylenediamine, methanediamine,isophoronediamine, 4,4′-diaminodicyclohexylmethane, andaminoethylenothanolamine. Preferred diamines are hydrazine, alkyl- orcycloalkyldiamines such as propylenediamine and1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane.

It is also possible to use polyamines containing more than two aminogroups in the molecule. In these cases, however, it should beensured—for example, by using monoamines as well—that no crosslinkedpolyurethane resins are obtained. Polyamines of this kind which may beused are diethylenetriamine, triethylenetetramine, dipropylenediamine,and dibutylenetriamine. An example of a monoamine is ethylhexylamine(cf. the patent BP-A-0 089 497).

Examples of suitable amino alcohols are ethanolamine or diethanolamine.

In the aqueous basecoat materials of the invention, the polyurethanes(A) are present advantageously in an amount of from 1.0 to 50%,preferably from 2.0 to 40%, with particular preference from 3.0 to 30%,with very particular preference from 4.0 to 25%, and in particular from5.0 to 20% by weight, based in each case on the overall weight of therespective aqueous basecoat material of the invention.

The further essential constituent of the coating material of theinvention is at least one crosslinking agent (B).

Examples of suitable crosslinking agents (B) are amino is resins,compounds or resins containing anhydride groups, compounds or resinscontaining epoxide groups, trig(alkoxycarbonylamino)triazines, compoundsor resins containing carbonate groups, blocked and/or nonblockedpolyisocyanates, beta-hydroxyalkylamides, and compounds containing onaverage at least two groups capable of transesterification, examplesbeing reaction products of malonic diesters and polyisocyanates or ofesters and partial esters of polyhydric alcohols of malonic acid withmonoisocyanates, as described by the European patent EP-A-0 596 460.

Crosslinking agents of this kind are well known to the skilled workerand are offered by numerous companies as sales products.

Examples of suitable polyepoxides are, in particular, all knownaliphatic and/or cycloaliphatic and/or aromatic polyepoxides, based forexample on bisphenol A or bisphenol P. Examples of suitable polyepoxidesalso include the polyepoxides available commercially under thedesignations Epikote® from Shell, Denacol® from Nagase Chemicals Ltd.,Japan, such as, for example, Denacol EX-411 (pentaerythritolpolyglycidyl ether), Denacol EX-321 (trimethylolpropane polyglycidylether), Denacol® EX-512 (polyglycerol polyglycidyl ether) and Denacol®EX-521 (polyglycerol polyglycidyl ether).

The suitable tris(alkoxycarbonylamino)triazines had the followingformula:

Examples of suitable tris(alkoxycarbonylamino)triazines are described inthe patents U.S. Pat. No. 4,939,213, U.S. Pat. No. 5,084,541 or EP-A-0624 577. Use is made in particular of the tris(methoxy-, tris(butoxy-and/or tris(2-ethylhexoxycarbonylamino)triazines.

Of advantage are the methyl butyl mixed esters, the butyl 2-ethylhexylmixed esters and the butyl esters. These have the advantage over thestraight methyl ester of better solubility in polymer melts, and alsohave less of a tendency to crystallize.

An example of a suitable polyanhydride is polysuccinic anhydride.

Examples of suitable beta-hydroxyalkylamides areN,N,N′,N′-tetrakis(2-hydroxyethyl)adipamide orN,N,N′,N′-tetrakis(2-hydroxypropyl)adipamide.

Further examples of suitable crosslinking agents are the blockedpolyisocyanates.

Examples of suitable blocking agents are the blocking agents known fromthe U.S. Pat. No. 4,444,954:

-   -   i) phenols such as phenol, cresol, xylenol, nitrophenol,        chlorophenol, ethylphenol, t-butylphenol, hydroxybenzoic acid,        esters of this acid or 2,5-di-tert-butyl-4-hydroxytoluene;    -   ii) lactams, such as ε-caprolactam, δ-valerolactam,        γ-butyrolactam or β-propiolactam;    -   iii) active methylenic compounds, such as diethyl malonate,        dimethyl malonate, ethyl or methyl acetoacetate or        acetylacetone;    -   iv) alcohols such as methanol, ethanol, n-propanol, isopropanol,        n-butanol, isobutanol, t-butanol, n-amyl alcohol, t-amyl        alcohol, lauryl alcohol, ethylene glycol monomethyl ether,        ethylene glycol monoethyl ether, ethylene glycol monobutyl        ether, diethylene glycol monomethyl ether, diethylene glycol        monoethyl ether, propylene glycol monomethyl ether,        methoxymethanol, glycolic acid, glycolic esters, lactic acid,        lactic esters, methylolurea, methylolmelamine, diacetone        alcohol, ethylenechlorohydrin, ethylenebromohydrin,        1,3-dichloro-2-propanol, 1,4-cyclohexyldimethanol or        acetocyanohydrin;    -   v) mercaptans such as butyl mercaptan, hexyl mercaptan, t-butyl        mercaptan, t-dodecyl mercaptan, 2-mercaptobenzothiazole,        thiophenol, methylthiophenol or ethylthiophenol;    -   vi) amides such as acetoanilide, acetoanisidinamide, acrylamide,        methacrylamide, acetamide, stearamide or benzamide;    -   vii) imides such as succinimide, phthalimide or maleimide;    -   viii) amines such as diphenylamine, phenylnaphthylamine,        xylidine, N-phenylxylidine, carbazole, aniline, naphthylamine,        butylamine, dibutylamine or butylphenylamine;    -   ix) imidazoles such as imidazole or 2-ethylimidazole;    -   x) ureas such as urea, thiourea, ethyleneurea, ethylenethiourea        or 1,3-diphenylurea;    -   xi) carbamates such as phenyl N-phenylcarbamate or        2-oxazolidone;    -   xii) imines such as ethyleneimine;    -   xiii) oximes such as acetone oxime, formaldoxime, acetaldoxime,        acetoxime, methyl ethyl ketoxime, diisobutyl ketoxime, diacetyl        monoxime, benzophenone oxime or chlorohexanone oximes;    -   xiv) salts of sulfurous acid such as sodium bisulfite or        potassium bisulfite;    -   xv) hydroxamic esters such as benzyl methacrylohydroxamate (BMH)        or allyl methacrylohydroxamate; or    -   xvi) substituted pyrazoles, ketoximes, imidazoles or triazoles;        and also    -   xvii) mixtures of these blocking agents, especially        dimethylpyrazole and triazoles, malonates and acetoacetates or        dimethylpyrazole and succinimide.

Examples of suitable organic polyisocyanates for blocking are inparticular the polyisocyanates known as paint polyisocyanates,containing aliphatically, cycloaliphatically, araliphatically and/oraromatically bonded isocyanate groups. Preference is given topolyisocyanates containing from 2 to 5 isocyanate groups per moleculeand having viscosities of from 100 to 10 000, preferably from 100 to 5000. Furthermore, the polyisocyanates can have been hydrophilically orhydrophobically modified in a customary and known way.

Further examples of suitable polyisocyanates for blocking are describedin “Methoden der organischen Chemie”, Houben-Weyl, Volume 14/2, 4^(th)edition, Georg Thieme Verlag, Stuttgart 1963, page 61 to 70, and by W.Siefken, Liebigs Annalen der Chemie, Volume 562, pages 75 to 136.Suitable examples include the polyurethane prepolymers containingisocyanate groups, which can be prepared by reacting polyols with anexcess of polyisocyanates and which are preferably of low viscosity.

Further examples of suitable polyisocyanates for blocking arepolyisocyanates containing isocyanurate, biuret, allophanate,iminooxadiazinedione, urethane, urea and/or uretdione groups.Polyisocyanates containing urethane groups, for example, are obtained byreacting some of the isocyanate groups with polyols, such astrimethylolpropane and glycerol, for example. It is preferred to usealiphatic or cycloaliphatic polyisocyanates, especially hexamethylenediisocyanate, dimerized and trimerized hexamethylene diisocyanate,isophorone diisocyanate, dicyclohexylmethane 2,4′-diisocyanate,dicyclohexylmethane 4,4′-diisocyanate, diisocyanates derived fromdimeric fatty acids, as marketed under the commercial designation DDI1410 by the company Henkel and described in the patents DO 97/49745 andWO 97/49747, especially2-heptyl-3,4-bis(9-isocyanatononyl)-1-pentylcyclohexane; or 1,2-, 1,4-or 1,3-bis(isocyanatomethyl)cyclohexane, 1,2-, 1,4- or1,3-bis(2-isocyanatoeth-1-yl)cyclohexane,1,3-bis(3-isocyanatoprop-1-yl)cyclohexane or 1,2-, 1,4- or1,3-bis(4-isocyanatobut-1-yl)cyclohexane,1,8-diisocyanato-4-isocyanatomethyloctane,1,7-diisocyanato-4-isocyanatomethylheptane or1-isocyanato-2-(3-isocyanatopropyl)cyclohexane, or mixtures of thesepolyisocyanates.

Very particular preference is given to using mixtures ofpolyisocyanurates which contain uretdione and/or isocyanurate groupsand/or allophanate groups that are based on hexamethylene diisocyanate,as formed by catalytic oligomerization of hexamethylene diisocyanateusing appropriate catalysts.

In particular it is possible to use amino resins, examples beingmelamine resins, guanamine resins or urea resins, as crosslinking agents(B). In this case it is possible to use any amino resin which issuitable for transparent topcoat materials or clearcoat materials, or amixture of such amino resins. For further details refer to Römpp LexikonLacke und Druckfarben, Georg Thieme Verlag, 1998, page 29, “Aminoresins”, and the textbook “Lackadditive” by Johan Bieleman, Wiley-VCH,Weinheim, N.Y., 1998, pages 242 ff., or to the book “Paints, Coatingsand Solvents”, second completely revised edition, Editors D. Stoye andW. Freitag, Wiley-VCH, Weinheim, N.Y., 1998, pages 80 ff. Also suitableare the customary and known amino resins some of whose methylol and/ormethoxymethyl groups have been defunctionalized by means of carbanate orallophanate groups. Crosslinking agents of this kind are described inpatents U.S. Pat. No. 4,710,542 and EP-B-0 245 700 and also in thearticle by B. Singh and coworkers, “Carbamylmethylated Melamines, NovelCroselinkers for the Coatings Industry” in Advanced Organic CoatingsScience and Technology Series, 1991, Volume 13, pages 193 to 207.

Preferably, the amino resins are contained in the aqueous basecoatmaterials of the invention as the predominant or sole crosslinkingagents (B). The other abovementioned crosslinking agents (B) can be usedas additional crosslinking agents (B) for the further advantageousvariation of the profile of properties of the aqueous basecoat materialsof the invention and of the inventive basecoats and inventive multicoatcolor and/or effect paint systems produced from them, their proportionamong the crosslinking agents (B) in that case being <50% by weight.

In the aqueous basecoat materials of the invention, the crosslinkingagents (B) are employed preferably in an amount of from 0.1 to 30%, morepreferably from 0.3 to 20%, with particular preference from 0.5 to 10%,and in particular from 1.0 to 8.0% by weight, based in each case on theoverall weight of the respective aqueous basecoat material of theinvention.

Yet another essential constituent of the aqueous basecoat material ofthe invention is at least one color and/or effect pigment (C). Thepigments (C) can be composed of organic or inorganic compounds. Theaqueous basecoat material of the invention therefore ensures, owing tothis large number of suitable pigments, a universal breadth of use, andpermits the realization of a large number of color shades and opticaleffects.

As effect pigments (C) it is possible to use metal flake pigments suchas commercial aluminum bronzes, aluminum bronzes chromated as perDE-A-36 36 183, commercial stainless steel bronzes, and nonmetalliceffect pigments, such as pearlescent pigments and interference pigments,for example. For further details refer to Römpp Lexikon Lacke undDruckfarben, Georg Thieme Verlag, 1998, pages 176, “Effect pigments” andpages 380 and 381, “Metal oxide/mica pigments” to “Metal pigments”.

Examples of suitable inorganic color pigments (C) are titanium dioxide,iron oxides, Sicotrans yellow, and carbon black. Examples of suitableorganic color pigments (C) are thioindigo pigments indanthrene blue,Cromophthal red, Irgazine orange and Heliogen green. For further detailsrefer to Römpp Lexikon Lacke und Druckfarben, Georg Thieme Verlag, 1998,pages 180 and 181, “Iron blue pigments” to “Black iron oxide”, pages 451to 453, “Pigments” to “Pigment volume concentration”, page 563“Thioindigo pigments” and page 567 “Titanium dioxide pigments”.

The fraction of the pigments (C) in the aqueous basecoat material of theinvention can vary extremely widely and is guided primarily by theopacity of the pigments (C), by the desired shade and by the desiredoptical effect. In the aqueous basecoat material of the invention, thepigments (C) are present in an amount of preferably from 0.5 to 50%,more preferably from 0.5 to 45%, with particular preference from 0.5 to40%, with very particular preference from 0.5 to 35%, and in particularfrom 0.5 to 30% by weight, based in each case on the overall weight ofthe aqueous basecoat material of the invention. The pigment/binderratio, i.e., the ratio of the pigments (C) to the above-describedpolyurethanes (A) or to the polyurethanes (A) and thehereinbelow-described polyacrylate resins (H) and polyesters (I), canalso vary extremely widely. This ratio is preferably from 4.0:1.0 to1.0:50, more preferably from 3.5:1.0 to 1.0:50, with particularpreference from 3.0:1.0 to 1.0:40, with very particular preference from2.5:1.0 to 1.0:30, and in particular from 2.3:1.0 to 1.0:25.

These pigments (C) may also be incorporated into the aqueous basecoatmaterials of the invention by way of pigment pastes, in which casesuitable dispersing resins include the above-described polyurethanes (A)and/or the hereinbelow-described polyacrylate resins (H) and/orpolyester resins (I).

Yet another essential constituent of the aqueous basecoat material ofthe invention is at least one inorganic thickener (E).

Examples of suitable inorganic thickeners (E) are inorganicphyllosilicates, preferably smectites, especially montmorillonites andhectorites, such as aluminum magnesium silicates, sodium magnesium andsodium magnesium fluorine lithium phyllosilicates of the montmorillonitetype or inorganic phyllosilicates such as aluminum magnesium silicates,aluminum magnesium silicates, sodium magnesium and sodium magnesiumfluorine lithium phyllosilicates of the montmorillonite type. Forfurther details, refer to the book by Johan Bielemann “Lackadditive”,Wiley-VCH, Weinheim, N.Y., 1998, pages 17 to 30.

In the aqueous basecoat materials of the invention, the thickeners (E)are present preferably in an amount of from 0.01 to 5.0%, morepreferably from 0.05 to 3.0%, with particular preference from 0.1 to2.5%, with very particular preference from 0.2 to 2.0%, and inparticular from 0.3 to 1.5% by weight, based in each case on the overallweight of the aqueous basecoat material of the invention.

In one preferred embodiment of the aqueous basecoat material of theinvention, it comprises in addition to the polyurethanes (A) at leastone water-soluble or -dispersible polyacrylate resin (H) prepared in thepresence of a water-soluble or -dispersible polyurethane.

Examples of suitable polyurethanes in whose presence the polyacrylateresin (H) is prepared contain olefinically unsaturated groups which arelateral, terminal and/or located within the main polymer chain, orcontain no olefinically unsaturated groups. Examples of highly suitablepolyurethanes of this kind are known from the patents EP-A-0 521 928,EP-A-0 522 420, EP-A-0 522 419 or EP-A-0 730 613 (olefinicallyunsaturated) or DE-A-44 37 535 (saturated). Examples of especiallysuitable polyurethanes are the above-described polyurethanes (A),especially the polyurethanes (A) containing carboxylic acid groupsand/or carboxylate groups.

Accordingly, the polyacrylate resins (H) which contain carboxylic acidgroups and/or carboxylate groups as solubilizing or dispersing groupsare of advantage in accordance with the invention and are therefore usedwith preference. As regards the neutralization of the polyacrylateresins (H), the comments made above in relation to the polyurethanes (A)apply analogously.

In accordance with the invention it is of advantage to prepare thepolyacrylate resins (H) in the presence of saturated polyurethanes (A),and so this variant is particularly preferred.

Very particularly highly suitable polyacrylate resins (H) are obtainedby copolymerizing the olefinically unsaturated monomers (h) describedbelow, of which at least one contains at least one carboxylic acid groupand preferably at least one contains at least one hydroxyl group and issubstantially free from acid groups.

Examples of suitable monomers (h) are:

Monomers (h1):

Hydroxyalkyl eaters of acrylic acid, methacrylic acid of anotheralpha,beta-ethylenically unsaturated carboxylic acid which are derivedfrom an alkylene glycol which is esterified with the acid, or areobtainable by reacting the acid with an alkylene oxide, especiallyhydroxyalkyl esters of acrylic acid, methacrylic acid or ethacrylic acidin which the hydroxyalkyl group contains up to 20 carbon atoms, such as2-hydroxyethyl, 2-hydroxypropyl, 3-hydroxypropyl, 3-hydroxybutyl,4-hydroxybutyl acrylate, methacrylate, ethacrylate or crotonate;1,4-bis(hydroxymethyl)cyclohexane,octahydro-4,7-methano-1H-indenedimethanol or methylpropanediolmonoacrylate, monomethacrylate, monoethacrylate or monocrotonate; orreaction products of cyclic esters, such as epsiloncaprolactone, forexample, and these hydroxyalkyl esters; or olefinically unsaturatedalcohols such as allyl alcohol or polyols such as trimethylolpropanemonoallyl or diallyl ether or pentaerythritol monoallyl, diallyl ortriallyl ether. These monomers (h1) of higher functionality aregenerally used only in minor amounts. In the context of the presentinvention, minor amounts of higher-functional monomers here are amountswhich do not result in the crosslinking or gelling of the polyacrylateresins. Thus, for example, the proportion of trimethylolpropanemonoallyl ether may be from 2 to 10% by weight, based on the overallweight of the monomers (h1) to (h6) used to prepare the polyacrylateresin. In addition, however, it is also possible to add from 2 to 10% byweight, based on the overall weight of the monomers (h) used to preparethe polyacrylate resin, of trimethylolpropane monoallyl ether to thefinished polyacrylate resin. Although the olefinically unsaturatedpolyols (h1) can be used as the sole monomers (h1), it is of advantagein accordance with the invention to use them in combination with furthermonomers (h1).

Monamers (h2):

(Meth)acrylic alkyl or cycloalkyl esters having up to 20 carbon atoms inthe alkyl radical, especially methyl, ethyl, propyl, n-butyl, sec-butyl,tert-butyl, hexyl, ethylhexyl, stearyl and lauryl acrylate ormethacrylate; cycloaliphatic (meth)acrylic esters, especiallycyclohexyl, isobornyl, dicyclopentadienyl,octahydro-4,7-methano-1H-indenemethanol or tert-butylcyclohexyl(meth)acrylate; (meth)acrylic oxaalkyl esters or oxacycloalkyl esterssuch as ethyltriglycol (meth)acrylate and methoxyoligoglycol(Tmeth)acrylate having a molecular weight Mn of preferably 550; or otherethoxylated and/or propoxylated hydroxyl-free (meth)acrylic acidderivatives. These may include, in minor amounts, higher-functional(meth)acrylic alkyl or cycloalkyl esters such as ethylene glycol,propylene glycol, diethylene glycol, dipropylene glycol, butyleneglycol, 1,5-pentanediol, 1,6-hexanediol,octahydro-4,7-methano-1H-indenedimethanol or cyclohexane-1,2-, -1,3- or-1,4-diol di(meth)acrylate; trimethylolpropane di- or tri(meth)acrylate;or pentaerythritol di-, tri- or tetra(meth)acrylate. In the context ofthe present invention, minor amounts of higher-functional monomers (h2)here are amounts which do not cause crosslinking or gelling of thepolyacrylate resins.

Monomers (h3):

Ethylenically unsaturated monomers which carry at least one acid group,preferably a carboxyl group, per molecule, or a mixture of suchmonomers. As component (h3) it is particularly preferred to use acrylicacid and/or methacrylic acid. It is also possible, however, to use otherethylenically unsaturated carboxylic acids having up to 6 carbon atomsin the molecule. Examples of such acids are ethacrylic acid, crotonicacid, maleic acid, fumaric acid, and itaconic acid. It is also possibleto use ethylenically unsaturated oulfonic or phosphonic acids, and/ortheir partial esters, as component (h3). Further suitable monomers (h3)include mono(meth)acryloyloxyethyl maleate, succinate, and phthalate.

Monomers (h4):

Vinyl esters of alpha-branched monocarboxylic acids having 5 to 18carbon atoms in the molecule. The branched monocarboxylic acids may beobtained by reacting formic acid or carbon monoxide and water witholefins in the presence of a liquid, strongly acidic catalyst; theolefins may be cracking products from paraffinic hydrocarbons, such asmineral oil fractions, and may contain both branched and straight-chainacyclic and/or cycloaliphatic olefins. In the reaction of such olefinawith formic acid and/or with carbon monoxide and water, a mixture ofcarboxylic acids is formed in which the carboxyl groups are locatedpredominantly on a quaternary carbon atom. Other olefinic startingmaterials are, for example, propylene trimer, propylene tetramer, anddiisobutylene. Alternatively, the vinyl esters may be prepared in aconventional manner from the acids; for example, by reacting the acidwith acetylene. Particular preference—owing to their readyavailability—is given to the use of vinyl esters of saturated aliphaticmonocarboxylic acids having 9 to 11 carbon atoms and being branched onthe alpha carbon atom.

Monomers (h5):

Reaction product of acrylic acid and/or methacrylic acid with theglycidyl ester of an alpha-branched monocarboxylic acid having 5 to 18carbon atoms per molecule. The reaction of the acrylic or methacrylicacid with the glycidyl ester of a carboxylic acid having a tertiaryalpha carbon atom may take place before, during or after thepolymerization reaction. As component (h5) it is preferred to use thereaction product of acrylic and/or methacrylic acid with the glycidylester of Versatic® acid. This glycidyl ester is obtainable commerciallyunder the name Cardura® E10. For further details, refer to Römpp LexikonLacke und Druckfarben, Georg Thieme Verlag, Stuttgart, N.Y., 1998, pages605 and 606.

Monomers (h6):

Ethylenically unsaturated monomers substantially free from acid groups,such as

-   -   olefins such as ethylene, propylene, 1-butene, 1-pentene,        1-hexene, cyclohexene, cyclopentene, norbornene, butadiene,        isoprene, cyclopentadiene and/or dicyclopentadiene;    -   (meth)acrylamides such as (meth)acrylamide, N-methyl-,        N,N-dimethyl-, N-ethyl-, N,N-diethyl-, N-propyl-, N,N-dipropyl,        N-butyl-, N,N-dibutyl-, N-cyclohexyl- and/or        N,N-cyclohexyl-methyl-(meth)acrylamide;    -   monomers containing epoxide groups, such as the glycidyl ester        of acrylic acid, methacrylic acid, ethacrylic acid, crotonic        acid; maleic acid, fumaric acid and/or itaconic acid;    -   vinylaromatic hydrocarbons, such as styrene, alpha-alkyltyrenes,        especially alpha-methylstyrene, arylstyrenes, especially        diphenylethylene, and/or vinyltoluene;    -   nitriles such as acrylonitrile and/or methacrylonitrile;    -   vinyl compounds such as vinyl chloride, vinyl fluoride,        vinylidene dichloride, vinylidene difluoride;        N-vinylpyrrolidone; vinyl ethers such as ethyl vinyl ether,        n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl        ether, isobutyl vinyl ether and/or vinyl cyclohexyl ether; vinyl        esters such as vinyl acetate, vinyl propionate, vinyl butyrate,        vinyl pivalate, vinyl esters of Versatic® acids, which are        marketed under the brand name VeoVa® by the company Deutsche        Shell Chemie (for further details, refer to Römpp Lexikon Lacke        und Druckfarben, Georg Thieme Verlag, Stuttgart, N.Y., 1998,        page 598 and also pages 605 and 606), and/or the vinyl ester of        2-methyl-2-ethylheptanoic acid; and/or    -   polysiloxane macromonomers having a number-average molecular        weight Mn of from 1 000 to 40 000, preferably from 2 000 to 20        000, with particular preference from 2 500 to 10 000, and in        particular from 3 000 to 7 000, and having on average from 0.5        to 2.5, preferably from 0.5 to 1.5, ethylenically unsaturated        double bonds per molecule, as are described in DE-A-38 07 571 on        pages 5 to 7, in DE-A-37 06 095 in columns 3 to 7, in EP-B-0 358        153 on pages 3 to 6, in U.S. Pat. No. 4,754,014 in columns 5 to        9, in DE-A-44 21 823, or in the international patent application        WO 92/22615 on page 12, line 18 to page 18, line 10, or        acryloxysilane-containing vinyl monomers, preparable by reacting        hydroxy-functional silanes with epichlorohydrin and then        reacting the reaction product with methacrylic acid and/or        hydroxyalkyl esters of (meth)acrylic acid.

In accordance with the invention it is especially advantageous to selectthe monomers (h) so as to give hydroxyl-containing polyacrylate resinswhich have an OH number of preferably from 0 to 200, more preferablyfrom 60 to 140, acid numbers of preferably from 20 to 100, morepreferably from 25 to 50, glass transition temperatures Tg of preferablyfrom −25 to +80° C., more preferably from −20 to +40° C., andnumber-average molecular weights of preferably from 1 500 to 30 000,more preferably from 1 500 to 20 000 (determined by gel permeationchromatography using polystyrene as internal standard).

The glass transition temperature Tg of the polyacrylate resins (H) isdetermined by the nature and amount of the monomers (h1) and, whereappropriate (h2), (h3), (h4), (h5) and/or (h6) that are used. Theskilled worker is able to select the monomers with the assistance of thefollowing formula of Fox, which can be used for approximate calculationof the glass transition temperatures Tg of (co)polymers, especiallypolyacrylate resins:$\quad{{{1\text{/}{Tg}} = {\underset{n = 1}{\overset{\overset{n = x}{.}}{a}}{Wn}\text{/}{Tg}_{n}}};\quad{{{\overset{.}{a}}_{n}W_{n}} = 1}}$Tg = glass  transition  temperature  of  the  polyacrylate  resinW_(n) = weight  fraction  of  the  nth  monomerTg_(n) = glass  transition  temperature  of  the  homopolymer  of  the  nthmonomer x = number  of  different  monomers

Viewed in terms of its method, the preparation of thehydroxyl-containing polyacrylate resins (H) for inventive use has nospecial features but instead takes place in accordance with thecustomary and known methods of radical polymerization in the presence ofat least one polymerization initiator.

Examples of suitable polymerization initiators are initiators which formfree radicals, such as tert-butylperoxyethyl hexanoate, benzoylperoxide, di-tert-amyl peroxide, azobisisobutyronitrile, and tert-butylperbenzoate. The initiators are used preferably in an amount of from 1to 25% by weight, with particular preference from 2 to 10% by weight,based on the overall weight of the monomers.

The polymerization is appropriately conducted at a temperature of from80 to 200° C., preferably from 110 to 180° C.

It is preferred to commence the initiator feed a certain time, generallyfrom about 1 to 15 minutes, before the monomers feed. Preference is alsogiven to a process wherein the addition of initiator is commenced at thesame time as the addition of the monomers and ended about half an hourafter the addition of the monomers has been ended. The initiator ispreferably added in a constant amount per unit time. After the end ofthe addition of initiator, the reaction mixture is held atpolymerization temperature until (generally 1.5 hours) all of themonomers used have undergone substantially complete reaction.“Substantially complete reaction” is intended to denote that,preferably, 100% by weight of the monomers used have been converted butthat it is also possible for a small residual monomer content of notmore than up to about 0.5% by weight, based on the weight of thereaction mixture, to remain unreacted.

One particularly preferred process for the preparation of thepolyacrylate resins (H) is described in DE-A-44 37 535.

In this process, in a first step, a polyurethane free fromcopolymerizable double bonds, especially a polyurethane (A), isintroduced in organic solution, after which a mixture of at least onemonomer (h1) and at least one monomer (h2) and also, where appropriate,in each case at least one monomer (h4), (h5) and/or (h6) is added, andthe mixture is copolymerized. After these monomers (h) have undergonealmost complete conversion, in a second process step a mixture of atleast one monomer (h3) and also in each case at least one monomer (h1)(h2), (h4), (h5) and/or (h6) is added, after which the resultingreaction mixture is polymerized to completion.

In terms of apparatus as well, the preparation of the polyacrylateresins (H) for inventive use has no special features as far as itsmethod is concerned but instead takes place with the aid of the methods,customary and known in the polymers field, of continuous or batchwisecopolymerization under atmospheric or superatmospheric pressure instirred tanks, autoclaves, tube reactors or Taylor reactors.

Examples of suitable copolymerization processes and apparatus aredescribed in the patents DE-A-197 09 465, DE-C-197 09 476, DE-A-28 48906, DE-A-195 24 182, EP-A-0 554 783, WO 95/27742 or WO 82/02387.

Following their preparation, the polyacrylate resins (H) are neutralizedwith at least one of the above-described suitable neutralizing agents(D), and dispersed in water. The total amount of neutralizing agent (D)used in the aqueous basecoat material of the invention is chosen suchthat from 1 to 100 equivalents, preferably from 50 to 90 equivalents, ofthe carboxyl groups of the polyurethanes (A) for inventive use and ofthe polyacrylate resins (H) are neutralized.

The fraction of the polyacrylate resins (H) in the aqueous basecoatmaterials of the invention can vary widely. It is preferably from 0.1 to10%, more preferably from 0.5 to 8.0%, with particular preference from0.6 to 6.0%, with very particular preference from 0.8 to 6.0%, and inparticular from 1.0 to 6.0% by weight, based in each case on the overallweight of the respective aqueous basecoat material of the invention.

In yet another preferred embodiment of the aqueous basecoat material ofthe invention, it comprises at least one water-soluble or -dispersiblepolyester resin (I).

Examples of suitable starting products for preparing the polyesterresins (I) are the compounds described above in connection with thepreparation of the polyester polyols.

Examples of suitable polyester resins (I) and their preparation fromsaid starting products are described in detail in the patents DE-A-40 09858 or DE-A-44 37 535.

The fraction of the polyester resins (I) in the aqueous basecoatmaterials of the invention can also vary widely. It is preferably from0.5 to 12%, more preferably from 0.7 to 10%, with particular preferencefrom 0.8 to 9.0%, with very particular preference from 1.0 to 8.0%, andin particular from 1.5 to 7.0% by weight, based in each case on theoverall weight of the respective aqueous basecoat material of theinvention.

In addition to the constituents described above, the aqueous basecoatmaterial of the invention may comprise customary and known additives (J)in effective amounts.

Examples of suitable additives (J) are

-   -   organic and inorganic fillers such as chalk, calcium sulfate,        barium sulfate, silicates such as talc or kaolin, silicas,        oxides such as aluminum hydroxide or magnesium hydroxide, or        organic fillers such as textile fibers, cellulose fibers,        polyethylene fibers or wood flour; for further details refer to        Römpp Lexikon Lacke und Druckfarben, Georg Thieme Verlag, 1998,        pages 250 ff., “Pillers”;    -   customary and known oligomeric and polymeric binders such as        thermally curable, hydroxyl-containing, linear and/or branched        and/or block, comb and/or random poly(meth)acrylates or acrylate        copolymers, polyesters, alkyds, acrylated polyesters,        polylactones, polycarbonates, polyethers, epoxy resin-amine        adducts, (meth)acrylate diols, partially hydrolyzed polyvinyl        esters, or polyureas;    -   customary and known thermally curable reactive diluents such as        positionally isomeric diethyloctanediols or hydroxyl-containing        hyper-branched compounds or dendrimers;    -   low-boiling and/or high-boiling organic solvents (“long        solvents”);    -   UV absorbers;    -   light stabilizers such as HPLLS compounds, benzotriazoles or        oxalanilides;    -   free-radical scavengers;    -   thermolabile free-radical initiators such as organic peroxides,        organic azo compounds or cleaving initiators such as dialkyl        peroxides, peroxocarboxylic acids, peroxodicarbonates, peroxide        esters, hydroperoxides, ketone peroxides, azo dinitriles or        benzpinacol silyl ethers;    -   crosslinking catalysts such as dibutyltin dilaurate, lithium        decanoate or zinc octoate, or amine-blocked organic sulfonic        acids;    -   devolatilizers, such as diazadicycloundecane;    -   slip additives;    -   polymerization inhibitors;    -   defoamers;    -   emulsifiers, especially nonionic emulsifiers such as alkoxylated        alkanols and polyols, phenols and alkylphenols or anionic        emulsifiers such as alkali metal salts or ammonium salts of        alkanecarboxylic acids, alkanesulfonic acids, and sulfo acids of        alkoxylated alkanols and polyols, phenols and alkylphenols;    -   wetting agents such as siloxanes, fluorine compounds, carboxylic        monoesters, phosphates, polyacrylic acids and their copolymers,        or polyurethanes;    -   adhesion promoters such as tricyclodecanedimethanol;    -   leveling agents;    -   film-forming auxiliaries such as cellulose derivatives;    -   transparent fillers based on silica, alumina, titanium dioxide        or zirconium oxide; for further details refer to Römpp Lexikon        Lacke und Druckfarben, Georg Thieme Verlag, Stuttgart, 1998,        pages 250 to 252;    -   other rheology control additives, such as those known from        patents WO 94/22968, EP-A-0 276 501, EP-A-0 249 201 or WO        97/12945; crosslinked polymeric microparticles, as disclosed for        example in EP-A-0 008 127; silicas such as Aerosils; or        synthetic polymers containing ionic and/or associative groups        such as polyvinyl alcohol, poly(meth)acrylamide,        poly(meth)acrylic acid, polyvinylpyrrolidone, styrene-maleic        anhydride or ethylene-maleic anhydride copolymers and their        derivatives or hydrophobically modified polyacrylates; and/or    -   flame retardants.

Further examples of suitable coatings additives are described in thetextbook “Lackadditive” by Johan Bieleman, Wiley-VCH, Weinheim, N.Y.,1998.

The aqueous basecoat materials of the invention preferably have a solidscontent at spray viscosity of from 5.0 to 60%, more preferably from 5.0to 50%, with particular preference from 10 to 45%, with very particularpreference from 13 to 40%, and in particular from 13 to 35% by weight,based in each case on the overall weight of the respective aqueousbasecoat material of the invention.

The preparation of the aqueous basecoat material of the invention has nospecial features but instead takes place in a customary and known mannerby mixing of the above-described constituents in appropriate mixingequipment such as stirred tanks, dissolvers or extruders in accordancewith the techniques suitable for preparing the respective aqueousbasecoat materials.

The aqueous basecoat material of the invention is used to produce thecoatings of the invention, especially multicoat paint systems, on primedor unprimed substrates.

Suitable substrates are all surfaces for coating which are not damagedby curing of the coatings present thereon using heat. Suitablesubstrates comprise, for example, the moldings, films and fibers of theinvention, metals, plastics, wood, ceramic, stone, textile, fiberassemblies, leather, glass, glass fibers, glass wool and rock wool,mineral-bound and resin-bound building materials, such as plasterboardpanels and cement slabs or roof shingles, and composites of thesematerials. The coating system of the invention, accordingly, is alsosuitable for applications outside of automotive finishing, particularlyautomobile finishing. In such applications it is suitable particularlyfor the coating of furniture and for industrial coating, including coilcoating, container coating, and the impregnation or coating ofelectrical components. In the context of industrial coatings it issuitable for coating virtually all parts for private or industrial usesuch as radiators, domestic appliances, small metal parts such as nutsand bolts, hubcaps, wheel rims, packaging, or electrical components suchas motor windings or transformer windings.

In the case of electrically conductive substrates it is possible to useprimers, which are prepared in a customary and known manner fromelectrocoat materials. Both anodic and cathodic electrocoat materialsare suitable for this purpose, but especially cathodics.

With the multicoat paint system of the invention it is also possible tocoat primed or unprimed plastics such as, for example, ABS, AMMA, ASA,CA, CAB, EP, UF, CF, MF, MPF, PF, PAN, PA, PE, HDPE, LDPE, LLDPE,UHMWPE, PET, PMMA, PP, PS, SB, PUR, PVC, RF, SAN, PBT, PPE, POM,PUR-RIM, SMC, BMC, PP-EPDM and UP (abbreviations to DIN 7728T1). Theplastics to be coated can of course also be polymer blends, modifiedplastics or fiber-reinforced plastics. It is also possible to employ theplastics that are commonly used in vehicle construction, especiallymotor vehicle construction.

In the case of unfunctionalized and/or a polar substrate surfaces, thesemay be subjected prior to coating in a known manner to a pretreatment,such as with a plasma or by flaming, or may be provided with awater-based primer.

The multicoat paint systems of the invention may be produced in avariety of ways.

A first preferred variant of the process of the invention comprises thefollowing steps:

-   -   (I) preparing a basecoat film by applying the aqueous basecoat        material of the invention to the substrate,    -   (II) drying the basecoat film,    -   (III) preparing a clearcoat film by applying a clearcoat        material to the basecoat film, and    -   (IV) jointly curing the basecoat film and the clearcoat film, to        give the basecoat and the clearcoat (wet-on-wet technique).

This variant offers particular advantages especially in the context ofthe coating of plastics, and is therefore employed with particularpreference in that utility.

A second preferred variant of the process of the invention comprises thefollowing steps:

-   -   (I) preparing a surfacer film by applying a surfacer to the        substrate,    -   (II) curing the surfacer film, to give the surfacer coat,    -   (III) preparing a basecoat film by applying the aqueous basecoat        material of the invention to the surfacer coat,    -   (IV) drying the basecoat film,    -   (V) preparing a clearcoat film by applying a clearcoat material        to the basecoat film, and    -   (VI) jointly curing the basecoat film and the clearcoat film, to        give the basecoat and the clearcoat (wet-on-wet technique).

A third preferred variant of the process of the invention comprises thefollowing steps:

-   -   (I) preparing a surfacer film by applying a surfacer to the        substrate,    -   (II) drying the surfacer film,    -   (III) preparing a basecoat film by applying the aqueous basecoat        material of the invention to the surfacer film,    -   (IV) drying the basecoat film,    -   (V) preparing a clearcoat film by applying a clearcoat material        to the basecoat film, and    -   (VI) jointly curing the surfacer film, the basecoat film and the        clearcoat film, to give the basecoat and the clearcoat (extended        wet-on-wet technique).

The two last-mentioned variants offer particular advantages especiallyin the context of the coating of automobile bodies and are thereforeemployed with very particular preference in that utility.

It is found here to be a further particular advantage of the aqueousbasecoat material of the invention and of the process of the inventionthat all customary and known clearcoat materials can be combined withthe aqueous basecoat film of the invention in the context of theprocesses of the invention.

Examples of suitable known one-component (1K), two-component (2K) ormulticomponent (3K, 4K) clearcoat materials are known from the patentsDE-A-42 04 518, U.S. Pat. No. 5,474,811, U.S. Pat. No. 5,356,669, U.S.Pat. No. 5,605,965, WO 94/10211, WO 94/10212, WO 94/10213, EP-A-0 594068, EP-A-0 594 071, EP-A-0 594 142, EP-A 0 604 992, WO 94/22969, EP-A-0596 460 or WO 92/22615.

One-component (1K) clearcoat materials are known to containhydroxyl-containing binders and crosslinking agents such as blockedpolyisocyanates, tris-(alkoxycarbonylamino)triazines and/or aminoresins. In another variant they include as binders polymers containingpendant carbamate and/or allophanate groups and carbamate- and/orallophanate-modified amino resin crosslinking agents (cf. U.S. Pat. No.5,474,811, U.S. Pat. No. 5,356,669, U.S. Pat. No. 5,605,965, WO94/10211, WO 94/10212, WO 94/10213, EP-A-0 594 068, EP-A-0 594 071 orEP-A-0 594 142).

Two-component (2K) or multicomponent (3K, 4K) clearcoat materialsinclude as essential constituents, as is known, hydroxyl-containingbinders and polyisocyanate crosslinking agents, which are storedseparately until they are used.

Examples of suitable powder clearcoat materials are known, for example,from the German patent DE-A-42 22 194 or from the BASF Lacke+Farbe AGproduct information bulletin “Pulverlacke”, 1990.

Powder clearcoat materials include as essential constituents, as isknown, binders containing epoxide groups, and polycarboxylic acidcrosslinking agents.

Examples of suitable powder slurry clearcoat materials are known, forexample, from the U.S. Pat. No. 4,268,542 and from the German patentapplications DE-A-195 18 392.4 and DE-A-196 13 547, or are described inthe German patent application DE-A-198 14 471.7, unpublished at thepriority date of the present specification.

Powder slurry clearcoat materials, as is known, comprise powderclearcoat materials in dispersion in an aqueous medium.

UV-curable clearcoat materials are disclosed, for example, by thepatents EP-A-0 540 884, EP-A-0 568 967 or U.S. Pat. No. 4,675,234.

Furthermore, the clearcoats may additionally be coated further with atleast one other clearcoat, an example being an organically modifiedceramic layer, thereby making it possible to improve significantly thescratch resistance of the multicoat paint system of the invention.

Accordingly, the multicoat paint systems of the invention can differ intheir structure.

In a first preferred variant of the multicoat paint system of theinvention, the following coats lie above one another in the statedorder:

-   -   (1) a surfacer coat which absorbs mechanical energy,    -   (2) the color and/or effect basecoat, and    -   (3) a clearcoat.

In the second preferred variant of the multicoat paint system of theinvention, the following coats lie above one another in the statedorder:

-   -   (1) the color and/or effect basecoat, and    -   (2) a clearcoat. This preferred variant is used in particular in        the coating of plastics.

The aqueous basecoat material of the invention may be applied by allcustomary application methods, such as spraying, knifecoating, brushing,flowcoating, dipping, impregnating, trickling, or rolling, for example.The substrates to be coated may itself be at rest, with the applicationequipment or unit being moved. Alternatively, the substrate to becoated, especially a coil, may be moved, with the application unit beingat rest relative to the substrate or being moved appropriately.

Preference is given to the use of spray application methods, such ascompressed-air spraying, airless spraying, high-speed rotation,electrostatic spray application (ESTA), alone or in conjunction with hotspray application such as hot-air spraying, for example. Application maybe conducted at temperatures of max. 70 to 80° C., so that suitableapplication viscosities are achieved without the short-term thermalstress being accompanied by any change in or damage to the aqueousbasecoat material or its overspray, which may be intended forreprocessing. For instance, hot spraying may be configured such that theaqueous basecoat material is heated in the spray nozzle for only a veryshort time, or is heated just a short way upstream of the spray nozzle.

The spray booth used for the application may be operated, for example,with an optionally temperature-controllable circulation, which isoperated with an appropriate absorption medium for the overspray, anexample being the aqueous basecoat material itself.

In general, the surfacer film, basecoat film and clearcoat film areapplied in a wet film thickness such that they cure to give coats havingthe coat thicknesses which are necessary and advantageous for theirfunctions. In the case of the surfacer coat, this coat thickness is from10 to 150, preferably from 15 to 120, with particular preference from 10to 100, and in particular from 10 to 90 μm; in the case of the basecoatit is from 5 to 50, preferably from 5 to 40, with particular preferencefrom 5 to 30, and in particular from 10 to 25 μm; and in the case of theclearcoats it is from 10 to 100, preferably from 1S to 80, withparticular preference from 20 to 70, and in particular from 25 to 60 μm.

The surfacer film, basecoat film and clearcoat film are cured thermally.

Full curing may take place after a certain rest time. Its duration maybe from 30 s to 2 h, preferably from 1 min to 1 h, and in particularfrom 1 min to 45 min. The rest time serves, for example, for the coatingfilms to flow and undergo devolatilization, or for the evaporation ofvolatile constituents such as solvents. The rest time may be assistedand/or shortened by the application of elevated temperatures of up to90° C. and/or by a reduced atmospheric humidity <10 g water/kg air,especially <5 g water/kg air, provided this does not entail any damageor change to the coating films, such as premature complete crosslinking,for instance.

The thermal curing has no special features in terms of its method butinstead takes place in accordance with the customary and known methods,such as heating in a convection oven or irradiation with IR lamps. Thisthermal curing may also take place in stages. Advantageously, thermalcuring takes place at a temperature of from 50 to 100° C., withparticular preference from 80 to 100° C., and in particular from 90 to100° C., for a time of from 1 min up to 2 h, with particular preferencefrom 2 min up to 1 h, and in particular from 3 min to 30 min. Ifsubstrates of high heat resistance are used, thermal crosslinking mayalso be conducted at temperatures above 100° C. In this case it isgenerally advisable not to exceed temperatures of 180° C., preferably160° C., and in particular 155° C.

In the case of clearcoats, depending on the clearcoat material used,curing may also take place with actinic radiation or both thermally andwith actinic radiation (dual cure). Suitable actinic radiation includeselectromagnetic radiation such as near infrared light (NIR), visiblelight, UV radiation or X-rays, and/or corpuscular radiation such aselectron beams.

The multicoat paint systems of the invention exhibit an outstandingprofile of properties which is very well balanced in terms of mechanics,optics, corrosion resistance, and adhesion. Thus the multicoat paintsystems of the invention possess the high optical quality and intercoatadhesion required by the market and do not give rise to any problemssuch as deficient surfacer-coat condensation resistance, cracking(mud-cracking) in the basecoats or leveling defects or surfacestructures in the clearcoats.

In particular, the multicoat paint system of the invention exhibit anoutstanding metallic effect, an excellent D.O.I. (distinctiveness of thereflected image), and an outstanding surface smoothness. They areweathering-stable, resistant to chemicals and bird droppings, arescratch resistant, and exhibits very good reflow behavior.

Not least, however, it proves to be a very special advantage that theuse of the aqueous basecoat materials of the invention in the productionof the multicoat paint systems of the invention results in only barelyvisible optical defects, if any.

Accordingly, the substrates coated with them have particular advantagessuch as a prolonged service life, a better esthetic impression on theviewer, and improved technological usefulness, so making themparticularly economically attractive.

EXAMPLES AND COMPARATIVE EXPERIMENTS Preparation Example 1

The Preparation of an Aqueous Polyurethane Dispersion (A)

716.6 parts by weight of a condensation product (number-averagemolecular weight: 1410) of 1.81 mol of a polymeric fatty acid (dimercontent at least 98% by weight, trimer content not more than 2.0% byweight, monomer content traces at most), 0.82 mol of isophthalic acid,0.61 mol of hexanediol and 0.61 mol of neopentyl glycol, 61 parts byweight of dimethylolpropionic acid, 10.6 parts by weight of neopentylglycol, 365 parts by weight of methyl ethyl ketone and 308.3 parts byweight of m-tetramethylxylylidene diisocyanate were heated at 80 degreesCelsius under nitrogen and with stirring in a suitable reaction vessel.Reaction was continued to an isocyanate content of 1.1% by weight, basedon the overall amount of reaction mixture. Subsequently 52.6 parts byweight of trimethylolpropane were added, after which the resultingreaction mixture was stirred at 80 degrees Celsius until free isocyanategroups were no longer detectable. Thereafter, slowly, 33 parts by weightof dimethylethanolamine, 255 parts by weight of butyl glycol and,subsequently, 2153 parts by weight of deionized water were stirred in.The methyl ethyl ketone was distilled off under reduced pressure. Thisgave a fine dispersion whose pH was adjusted to 7.4 usingdimethylethanolamine and whose nonvolatiles fraction was adjusted to 31%by weight using deionized water.

Preparation Example 2

The Preparation of an Aqueous Polyester Resin Solution (I)

A reactor equipped with stirrer, thermometer and packed column wascharged with 729 parts by weight of neopentyl glycol, 768 parts byweight of hexanediol, 462 parts by weight of hexahydrophthalic anhydrideand 1710 parts by weight of a polymeric fatty acid (dimer content atleast 98% by weight, trimer content not more than 2% by weight, monomercontent traces at most), and this initial charge was melted. Theresulting melt was heated with stirring in such a way that the overheadcolumn temperature did not exceed 100 degrees Celsius. Esterificationwas carried out at 220 degrees Celsius maximum until an acid number of 9was reached. After the mixture had cooled to 180 degrees Celsius, 768parts by weight of trimellitic anhydride were added and esterificationwas continued until an acid number of 32 was reached. Thereafter, thereaction mixture was cooled to 120 degrees Celsius and diluted with 1392parts by weight of butyl glycol. After it had cooled to 90 degreesCelsius, 158 parts by weight of dimethylethanolamine were stirred inslowly, followed by 1150 parts by weight of deionized water. Theresulting polyester resin solution was adjusted to a pH of 7.6 usingdimethylethanolamine and to a nonvolatiles fraction of 60% by weightusing deionized water.

Preparation Example 3

The Preparation of a Polyacrylate Resin (H)

500 parts by weight of a condensation product (number-average molecularweight: 1423) of 1.0 mol of a polymeric fatty acid (dimer content atleast 98% by weight, dimer content not more than 2.0% by weight, monomercontent traces at most), 1.5 mol of isophthalic acid, 1.6 mol ofneopentyl glycol and 1.7 mol of hexanediol, 31.2 parts by weight ofneopentyl glycol, 185 parts by weight of methyl ethyl ketone, 201.7parts by weight of m-tetramethylxylylidene diisocyanate and 0.7 part byweight of dibutyltin dilaurate were heated at 80 degrees Celsius undernitrogen and with stirring. The reaction was continued to an isocyanatecontent of 1.3% by weight, based on the overall amount of reactionmixture. Thereafter, 30 parts by weight of diethanolamine were added andthe resulting reaction mixture was stirred at 80 degrees Celsius untilisocyanate groups were no longer detectable. Subsequently, 466 parts byweight of butyl glycol were stirred in, after which the methyl ethylketone was distilled off under reduced pressure. The resultingpolyurethane solution was then adjusted to a nonvolaciles fraction of60% by weight using butyl glycol.

A steel vessel equipped with monomer feed, initiator feed, thermometer,oil heating and reflux condenser was charged with 28.44 parts by weightof butyl glycol and 24.24 parts by weight of the abovementionedpolyurethane solution, and this initial charge was heated to 110 degreesCelsius. Then a solution of 5.1 parts by weight of t-butylperethylhexanoate in 6.0 parts by weight of butyl glycol was addeduniformly at a rate such that the addition was over after 5.5 hours. Thebeginning of the addition of initiator was also accompanied bycommencement of the addition of a mixture of 18.36 parts by weight ofn-butyl mathacrylate, 17 parts by weight of methyl methacrylate, 17parts by weight of lauryl methacrylate, 17.34 parts by weight ofhydroxypropyl acrylate and 12.75 parts by weight of styrene. The monomermixture was added uniformly at a rate such that the addition was over infive hours. After all of the initiator solution had been added, thereaction mixture was held at 110 degrees Celsius for a further hour.

Subsequently, a solution of 1.17 parts by weight of t-butylperethylhexanoate in 3.5 parts by weight of butyl glycol was addeduniformly at a rate such that the addition was over after 1.5 hours. Thebeginning of the addition of the initiator solution was also accompaniedby the commencement of addition of a mixture of 5.85 parts by weight ofacrylic acid and 4.65 parts by weight of n-butyl methacrylate, 2.94parts by weight of methyl methacrylate, 5.90 parts by weight of laurylmethacrylate, 1.25 parts by weight of hydroxypropyl acrylate and 2.94parts by weight of styrene. The monomer mixture was added uniformly at arate such that the addition was over within one hour. Thereafter, thetemperature of the reaction mixture was held at 110 degrees Celsius for1.5 hours more. The resulting resin solution was concentrated bydistillation under reduced pressure to a solids content of 80% by weightand at this temperature was neutralized with dimethylethanolamine overthe course of 30 minutes to a degree of neutralization of 80%. The resinsolution was cooled to 60 degrees Celsius, after which the heating wasshut off. Then water was added slowly until the solids content of thedispersion was 40% by weight. The dispersion had an acid number of 36.7mg KOH/g and a pH of 7.6.

Examples 1 and 2 and Comparative Exeriments C1 and C2

The Preparation of Inventive (Examples 1 and 2) and Noninventive(Comparative Exeriments C1 and C2) Aqueous Basecoat Materials

The preparations of the inventive aqueous basecoat materials of examples1 and 2 and of the noninventive aqueous basecoat material of comparativeexperiment C2 were conducted in analogy to the preparation instructionsindicated below for the noninventive aqueous basecoat material ofcomparative experiment C1. Table 1 gives an overview of the amounts ofthe starting products employed.

For comparative experiment C1, the thickener 1 (paste of a syntheticsodium magnesium phyllosilicate from Laporte; 3% in water) wasintroduced initially. Added to this with stirring were deionized water,thickener 3 (3% aqueous solution of a polyacrylic acid from AlliedColloids; trade name: Viscalex), the polyurethane dispersion (A) frompreparation example 1, the polyester resin solution (I) from preparationexample 2, the solution of the polyacrylate (H) from preparation example3, butyl glycol, a commercial melamine resin in butanol (Maprenal®VMF3924), a silica filler paste (12 parts by weight of Syloid® ED-3 fromGrace; 30 parts by weight of the abovementioend polyester resin solution(I)), a neutralizing agent (D) (dimethylethanolamine, 10% in water), asolution of a commercial defoamer based on alkynediol (50% in butylglycol; from Air Products), deionized water, a pigment paste 1 (63 partsby weight of polyurethane dispersion, 31 parts by weight of titaniumrutile Tayca® MT500HD from Tayca), a pigment paste 2 (64 parts by weightof polyurethane dispersion and 32 parts by weight of titanium dioxideUVL 530 from Kemira).

Prepared separately from this was an aluminum pigment slurry composed of5.0 parts by weight of a commercial aluminum paste (Alu-Stapa-Hydrolux®2192 from Eckart), 6.0 parts by weight of solvent and 2.4 parts byweight of the polyester resin solution (I). This aluminum pigment slurrywas stirred into the mixture described above.

The resultant mixture was then neutralized to a pH of about 8.0 usingthe neutralizing solution (D) and was adjusted using deionized water toa viscosity of 65 mPas under a shear of 1291 s⁻¹.

For comparative experiment C2, comparative experiment C1 was repeatedbut using the thickener 2 instead of the thickener 1. Said thickener 2is a 3% solution of a synthetic sodium magnesium phyllosilicate fromSü{umlaut over ( )}dchemie.

For example 1, comparative experiment C1 was repeated but using thethickener 4 instead of the thickener 3. Said thickener 4 is a mixture of50% by weight of a polyurethane-based associative thickener (G) (Nopco®DSX1550 from Henkel) and 50% by weight of butyl glycol.

For example 2, example 1 was repeated but using, instead of butylglycol, dipropylene glycol monoalkyl ether for the preparation of thealuminum pigment slurry.

The aqueous basecoat materials of comparative experiment C2 and ofexamples 1 and 2 were also adjusted using neutralizing solution (D) to apH of about 8.0 and using deionized water to a viscosity of 65 mPasunder a shear of 1291 s⁻¹.

Table 1 gives an overview of the amounts of the starting products and ofthe composition of the aqueous basecoat materials.

TABLE 1 The composition of the inventive (examples 1 and 2) and of thenoninventive (comparative experiments C1 and C2) aqueous basecoatmaterials Comparative experiments: Examples: Constituents C1 C2 1 2Thickener 1 29 — 29 29 Thickener 2 — 29 — — Deionized water 9.0 9.0 9.09.0 Thickener 3 5.5 5.5 — — Polyurethane dispersion (A) 21.5 21.5 21.521.5 Polyester solution (I) 2.0 2.0 2.0 2.0 Polyacrylate resin solution(H) 5.0 5.0 5.0 5.0 Butyl glycol 2.0 2.0 2.0 2.0 Melamine resin (B) 5.05.0 5.0 5.0 Filler paste 1.2 1.2 1.2 1.2 Neutralizing agent (D) 0.4 0.40.4 0.4 Defoamer 2.0 2.0 2.0 2.0 Thickener 4 — — 1.6 1.6 Deionized water4.0 4.0 4.0 4.0 Pigment paste 1 4.3 4.3 4.3 4.3 Pigment paste 2 0.8 0.80.8 0.8 Alu-Stapa-Hydrolux ® 5.0 5.0 5.0 5.0 Butyl glycol 6.0 6.0 6.0 —Dipropylene glycol methyl ether — — — 6.0 Polyester solution (I) 2.4 2.42.4 2.4

The viscosity behavior of the inventive (examples 1 and 2) and of thenoninventive (comparative experiments C1 and C2) aqueous basecoatmaterials was measured under different shear rates. The results can befound in tab. 2.

TABLE 2 The viscosity behavior of the inventive (examples 1 and 2) andof the noninventive (comparative experiments C1 and C2) aqueous basecoatmaterials Viscosity (mPas): Comparative experiments: Examples Shear rate(s⁻¹) C1 C2 1 2 34 (outgoing curve) 360 220 355 350 1000 73 73 73 73 34(return curve) 250 180 245 235

The values from table 2 demonstrate that the aqueous basecoat materialsof examples 1 and 2 and of comparative experiments C1 and C2 had acomparable (comparative experiment C2 on the one hand and examples 1 and2 and comparative experiment C1 on the other) or identical (examples 1and 2 and comparative example C1) viscosity behavior.

Examples 3 and 4 and Comparative Experiments C3 and C4

Testing of the Inventive (Examples 3 and 4) and of the Noninventive(Comparative Experiments C3 and C4) Aqueous Basecoat Materials for TheirAction Against the Formation of Optical Defects

For example 3, the inventive aqueous basecoat material of example 1 wasused.

For example 4, the inventive aqueous basecoat material of example 2 wasused.

For comparative experiment C3, the noninventive aqueous basecoatmaterial of comparative experiment C1 was used.

For comparative experiment C4, the noninventive aqueous basecoatmaterial of comparative experiment C2 was used.

The test panels of examples 3 and 4 and of comparative experiments C3and C4 were prepared in accordance with the following generalinstructions:

Steel panels coated cathodically with a commercial electrocoat material(electrocoat with a thickness of 18-22 μm) were first coated with acommercial filler from BASF Coatings AG, using a cup-type gun, andbaked.

This gave a surfacer with a thickness of from 35 to 40 μm. Atop thesurfacer there were then applied, in the same way, the inventive and thenoninventive aqueous basecoat materials (cf. table 1), which werepredried at 80° C. for 10 minutes. Following the cooling of the panels,a coat of commercial two-component high-solids clearcoat material fromDuPont was applied in each case, predried at room temperature for 10minutes, and then crosslinked together with the basecoats at 140° C. for45 minutes. This gave basecoats with a thickness of 15 μm and clearcoatswith a thickness of 44 μm.

1. Light Spots

In the wet sanding of defects in an original finish or in a surfacer,water droplets remain on the parts of the body that are to be overcoatedwith basecoat and clearcoat. These water droplets are made up of water,abrasion dust from clearcoat and/or surfacer, and residues of theabrasive paper. Following the drying of these water droplets andsubsequent coating with the basecoat and clearcoat, the sites of thedried-out water are visible as light (-colored) spots.

In order to simulate this effect, abrasion water droplets (deionizedwater+abrasion dust from surfacer and clearcoat+abrasive paper fromPlochmann, softened in this composition) of various sizes were appliedto the respective test panels, dried at room temperature and coated withthe respective basecoat materials employed for the original finish anddescribed in table 1 and with the two-component high-solids clearcoatmaterial from DuPont. The resulting color differences in the coatings(light spots) were assessed visually. The results obtained can be foundin table 3.

2. Polishing Spots

Polishing sites were produced on the test panels using a red/white feltpad (Buffing Pad from 3M, No. 049-5765) and the gray polishing pastefrom 3M (No. 029-2778). In the subsequent coating with the basecoatmaterials described in table 1 and the abovementioned clearcoatmaterial, these polishing sites were clearly visible on account of theirdifferent color. The respective difference in color was determinedvisually. The results obtained can be found in table 3.

3. Abrasion Spots

Using an abrasive paper from Plochmann with a grade of 2000, both around and a cross-shaped abrasion site were applied to the test panels.These abrasion sites were coated with the basecoat materials describedin table 1 and with the abovementioned clearcoat material.

The respective color difference was determined visually. The resultsobtained can be found in table 3.

The color difference, i.e., the obviousness of the defects, was scoredas follows:

Rating Meaning

-   -   1 defects not visible    -   2 defects very slightly visible    -   3 defects slightly visible    -   4 defects markedly visible    -   5 defects very markedly visible

TABLE 3 The effect of the inventive (examples 3 and 4) and of thenoninventive (comparative experiments C3 and C4) aqueous basecoatmaterials on the formation of optical defects Comparative experiments:Examples: Optical defects C3 C4 3 4 Light spots 4 5 2 2 Polishing spots4 5 4 2-3 Abrasion spots 3-4 4 2-3 2

The results demonstrate that by means of the aqueous basecoat materialsof the invention the formation of optical defects can be effectivelysuppressed.

An additional improvement results from the use of dipropylene glycolmonoalkyl ether. The comparison of the results in table 3 with theaqueous basecoat material viscosity behavior shown in the overview intable 2 underlines the fact that said behavior, surprisingly, is notresponsible for the advantageous effect of the aqueous basecoatmaterials of the invention.

1. A method for supressing optical defects in a paint system, whereinthe paint system is one of a multicoat color paint system, a multicoateffect paint system, a multicoat color and effect paint system, a colorrefinish paint system, an effect refinish paint system, and a color andeffect refinish paint system, comprising including an associativethickener in the paint system, wherein the associative thickenercomprises a dipropylene glycol monoalkyl ether and optionally apolyurethane-based associative thickener, wherein the alkyl in thedipropylene glycol monoalkyl ether is at least one of n-pentyl andn-hexyl.
 2. The method of claim 1, wherein the paint system comprises atleast one basecoat layer and at least one clearcoat layer.
 3. The methodof claim 2, wherein the basecoat layer is produced from an aqueousbasecoat material.
 4. The method of claim 3, wherein the aqueousbasecoat material comprises a polyurethane polymer.
 5. The method ofclaim 1, wherein the associative thickener is present in a basecoatlayer.
 6. The method of claim 1, wherein the polyurethane-basedassociative thickener and the dipropylene glycol monoalkyl ether arepresent in a basecoat layer.
 7. The method of claim 1, wherein theoptical defects comprise at least one of: i) light-colored spots,introduced by at least one of dried-up liquid residues and abrasion dustresidues, which remain after abrading of defects in the paint system orin a surfacer that is to be coated with the paint system; and ii)polishing spots, induced by the polishing of defects in the paintsystem, which is performed for the purpose of refinishing the paintsystem.
 8. The method of claim 3, wherein the aqueous basecoat materialcomprises (A) at least one water-soluble or -dispersible polyurethane,(B) at least one crosslinking agent, (C) at least one pigment that is atleast one of a color pigment, an effect pigment, and a color and effectpigment, (D) at least one neutralizing agent, (E) at least one inorganicthickener, (F) an associative thickener comprising a dipropylene glycolmonoalkyl ether and optionally a polyurethane-based associativethickener, wherein the alkyl in the dipropylene glycol monoalkyl etheris at least one of n-pentyl and n-hexyl, (G) optionally, at least onewater-soluble or -dispersible polyacrylate resin prepared in thepresence of a water-soluble or -dispersible polyurethane, and (H)optionally, at least one water-soluble or -dispersible polyester resin.9. The method of claim 8, wherein the aqueous basecoat material, basedon its overall weight, contains from 0.5 to 11% by weight of thedipropylene glycol monoalkyl ether.
 10. The method of claim 8, whereinthe aqueous basecoat material, based on its overall weight, containsfrom 0.1 to 4% by weight of the polyurethane-based associativethickener.
 11. The method of claim 8, wherein the aqueous basecoatmaterial further comprises at least one additive.
 12. The paint systemprepared by the process of claim
 1. 13. The paint system of claim 12,wherein the paint system is one of an original coating for a motorvehicle body, an industrial coating, an electrical components coating, acoil coating, a packaging coating, a plastics coating, and a furniturecoating.
 14. An aqueous basecoat material comprising (A) at least onewater-soluble or -dispersible polyurethane, (B) at least onecrosslinking agent, (C) at least one pigment that is at least one of acolor pigment, an effect pigment, and a color and effect pigment, (D) atleast one neutralizing agent, (E) at least one inorganic thickener, (F)an associative thickener comprising a dipropylene glycol monoalkyl etherand optionally a polyurethane-based associative thickener, wherein thealkyl in the dipropylene glycol monoalkyl ether is at least one ofn-pentyl and n-hexyl, (G) optionally, at least one water-soluble or-dispersible polyacrylate resin prepared in the presence of awater-soluble or -dispersible polyurethane, and (H) optionally, at leastone water-soluble or -dispersible polyester resin.
 15. The aqueousbasecoat material of claim 14, wherein the aqueous basecoat material,based on its overall weight, contains 0.5 to 11% by weight of thedipropylene glycol monoalkyl ether.
 16. The aqueous basecoat material ofclaim 14, wherein the aqueous basecoat material, based on its overallweight, contains from 0.1 to 4% by weight of the polyurethane-basedassociative thickener.
 17. The aqueous basecoat material of claim 14further comprises at least one additive.
 18. A paint system comprisingat least one basecoat layer; wherein the paint system is one of amulticoat color paint system, a multicoat effect paint system, asmulticoat color and effect paint system, a color refinish paint system,an effect refinish paint system, and a color and effect refinish paintsystem; and wherein the basecoat layer is produced from the aqueousbasecoat material of claim 14.